1. Field of the Invention
The present invention relates generally to thin film technology and, more particularly, to anti-contamination shields and collimators for thin film process apparatus.
2. Description of the Related Art
In thin film deposition and etch processes, such as physical vapor deposition ("PVD"), or "sputtering," a target material is bombarded by high energy gaseous ions. Material from the target is dislodged and sputters onto a work piece. The work piece may be, as examples, a semiconductor wafer, a magnetic disk, or a flat panel display.
For example, a PVD chamber, such as shown in FIGS. 1A and 1B (Prior Art) usually includes a chamber apparatus 14 generally constructed of stainless steel. A shield 19, generally constructed of aluminum, is mounted to the chamber directly or through use of an adapter 17 (also constructed of stainless steel) fitted appropriately to conform the chamber cavity. A clamping ring 16 is also sometimes employed in such apparatus.
The shield 19 is of an appropriate size and shape to protect the chamber cavity. For example, during the course of thin film processing, a work piece 36, such as a semiconductor wafer, is placed within the PVD chamber 14 through an opening 31 by automated machinery. A wafer table 25 is raised into a target location through the shield 19 to a position where PVD processing occurs. As a DC-biased target 30 on source 20 (electrically isolated by insulator 28) is bombarded by ions (such as argon) generated by a plasma created between the DC-biased target 30 and the work piece 36, target atoms are ejected within the chamber 14 and onto the work piece 36. The shield 19 prevents excess material sputtering from the target 30 from contaminating the remainder of the PVD chamber interior. Substantial heat is generated during this process, raising the temperature of the shield 19 and the chamber apparatus 14. The shield 19 is replaced once the build-up of excess target material reaches a point where flaking may impair further PVD processes.
Note that prior art type shields generally do not fully contact the chamber walls or adapter 17 during work piece processing. The shield 19 can be bolted to an adapter 17. FIG. 2 (Prior Art) shows the typical components of the shield 19 and adapter 17 subsystem and mounting bolts 21 that affix the shield 19 to the adapter 17. This procedure does not provide a good thermal coupling between the shield 19 and the adapter 17 or the chamber walls. During high power thin film processes (for example, aluminum or collimated titanium-nitride deposition), the shield may reach temperatures as high as 300 to 500 degrees Centigrade. The thermal expansion of the shield material can cause buckling or warping of the shield 19. In such buckled or warped regions, the shield 19 loses contact with the adapter 17 or the inner chamber walls, deteriorating even further the already poor thermal coupling. Excessive thermal expansion may contribute to the harmful contamination of the work piece 36.
Other shield mounting techniques, such as brazing or welding could provide good thermal contact, but are impractical within production PVD systems as they make removal and replacement difficult.
Forced temperature maintenance, such as by water cooling the shield during high temperature processes, not only increases the complexity and cost of the system, but also risks the introduction of water vapor into the PVD chamber which is highly destructive to the PVD process itself.
There is a need, therefore, for an improved mounting of an anti-contamination shield for thin film process systems. As will be disclosed with respect to an alternative embodiment, the same principles apply to collimator plates used in collimated PVD processes. The same inventive principles can apply to any deposition and etch system where shielding is used to protect chamber walls from deposited or etched material and where significant heat has to be removed from the active inner portion of the chamber.